1. Field of the Invention
The present invention generally relates to apparatus and methods for treatment of human bone. Embodiments of the invention relate to spinal stabilization systems and methods that may be used to treat damaged or diseased bone. Embodiments of the invention relate to systems and methods used to augment fixation of bone fasteners. Embodiments of the invention relate to systems and methods used in vertebroplasty.
2. Description of Related Art
Bone may be treated for damage or degeneration arising from a variety of causes, such as trauma, disease, and/or aging. For example, stabilization of a spine may involve implantation of a system to provide fixation of a portion of the spinal column. As another example, treatment of diseased bone tissue (e.g., a bone tumor) may involve removal of the tumor followed by stabilization procedures to strengthen and/or support remaining bone.
Weakened or softened bone may be difficult to treat with conventional stabilization techniques. For example, spinal stabilization procedures may fail in osteoporotic vertebrae. Osteoporosis (i.e., a bone condition characterized by reduction in bone mass and increased susceptibility to fracture after minimal trauma) may cause loosening and/or pullout of bone fasteners, possibly leading to failure of the spinal stabilization system. Pullout strength may be increased by introducing bone cement (e.g., polymethylmethacrylate) into bone proximate a bone fastener. U.S. Pat. No. 6,565,572 to Chappius, which is incorporated by reference as if fully set forth herein, describes a fenestrated surgical screw. The design allows material to be delivered through a passage in a body of the screw into a skeletal member. Holes in the shank of the screw communicate with the passage and allow injected bone cement to pass into bone surrounding the screw. After curing, the bone cement fixes the screw in place in the bone. A fenestrated bone screw that has been cured in place may be difficult to remove should a subsequent procedure be necessary due to infection, further injury, and/or other causes.
Treatment for fractured or diseased bone may include minimally invasive procedures such as vertebroplasty. In a vertebroplasty procedure, bone cement may be injected into a vertebra to stabilize a fracture and relieve pain associated with the fracture. Other treatments may include steps to restore a natural height of a fractured vertebra followed by injection of bone cement or other material into a cavity in the vertebra. For example, a surgeon may use an inflatable balloon to compact bone, then inject a biomaterial into a cavity. Such balloon procedures have been referred to as “kyphoplasty,” and equipment for such procedures may be available from Kyphon, Inc.
One method for introducing bone cement into a vertebra is through a biopsy needle (e.g., a Jamshidi® needle) inserted in an opening in the bone. Limitations of such methods of cement introduction may include retrograde flowback of bone cement along the needle and limited vertebral body fill. Local complications from bone cement leakage (i.e., retrograde flowback) may include radiculopathy and cord compression. Systemic complications from bone cement leakage may include fever, infection, pulmonary embolism, fat embolism, hypoxia, hypotension, myocardial infarction, and sudden death.